1. Field of the Invention
The present invention relates to a method and a device for the manufacture of a sealing gasket on the rim of a sheet of glass, particularly of a sheet of glass to be used as glazing on a vehicle or a fixed installation.
The method is well known of manufacturing a sealing gasket for a sheet of glass directly on the outer rim of the glass.
2. Description of the Prior Art
Italian patent 1178437 in particular describes a process comprising the step of injecting a thermosetting polyurethane material into the cavity of a mold placed all around the rim of the sheet of glass to be provided with a sealing gasket. The injected polyurethane material polymerizes at predetermined temperature and pressure conditions and adheres to the rim of the glass thus taking the shape of the cavity into which it was injected.
Italian patent 1178177 describes a mold for carrying out the process according to the above mentioned patent. The mold comprises two portions complementary one to the other, which, on closing one on the other, define a cavity to receive the polyurethane material, injected through a hole. A sealing junction placed in a predetermined position in each of the mold portion and around the cavity is used to prevent the injected material from pouring onto the glass surface.
By means of the above mentioned process it is possible to manufacture in one step the entire sealing gasket on a sheet of glass, the sealing gasket serving the purpose of supporting and sealing the glass on the structure to which it is assembled, as well as aesthetically merging the glass surface into the same structure.
The above mentioned known prior art shows, however, some disadvantages.
The polyurethane material forming the sealing gasket does not withstand weathering satisfactorily, so that the strip surface which, after assembling, is in contact with the outer environment, tends to degrade. Consequently a further operation after injection and polymerization is provided, which consists in painting the exposed surface with an opaque paint.
The two complementary half-molds have to be provided with a sealing junction in the areas in which they are in contact with the glass. These sealing junctions are subjected to wear and to damage, so that they have to be replaced from time to time.
Since the half-mold forming the outer part of the sealing gasket should provide the gasket with a particular finishing and precision working, and thus also has an aesthetic function, such a half-mold has to be carefully cleaned after each cycle of molding to prevent unacceptable surface defects.
The inner surface of both half-molds should be treated regularly with anti-adhesive products to avoid, during the molding, portions of the sealing gasket remaining glued to the mold, which would result in a production of waste and further loss of time for the cleaning of the mold.